4.1 RATES OF REACTION

Question 1

what is activation energy?

Answer 1

the amount of energy the particles need to react

Question 2

what happens to particles with insufficient activation energy?

Answer 2

collide with each other and rebound and remain unchanged

Question 3

what does the overall rate of reaction depend on?

Answer 3

• collision frequency
• percentage success

Question 4

why does higher surface area increase rate?

Answer 4

• more of the solid is exposed to other particles
• so there is a higher frequency of collisions
• so there are more successful collisions per unit of time

Question 5

why does higher solution concentration/gas pressure increase rate?

Answer 5

• there are more particles per unit volume
• so the collision frequency is higher
• so there are more successful collisions per unit of time

Question 6

why does higher temperature increase rate?

Answer 6

• the particles have more kinetic energy
• so the percentage of collisions with enough energy is higher
• so there are more successful collisions per unit of time

Question 7

why do catalysts increase rate?

Answer 7

• they provide an alternate route with lower activation energy
• so the percentage of collisions with enough energy is higher
• so there are more successful collisions per unit of time

Question 8

what is a catalyst?

Answer 8

a substance that increases the rate of reaction but is chemically unchanged at the ned of the reaction

Question 9

what does a catalyst provide?

Answer 9

an alternate pathway with lower activation energy

Question 10

practical: investigate the effects of changing the surface area of marble chips and of changing the concentration of hydrochloric acid on the rate of reaction between marble chips and dilute hydrochloric acid:

Answer 10

• INPUT- the size of the CaCO3 (s) chips
• OUTPUT- volume of CO2
• CONTROL- mass of CaCO3, volume and concentration of HCl, temperature

Question 11

practical: marble chip experiment results:

Answer 11

smaller chips (higher surface area) increases rate of reaction but produces the same amount of CO2 in the end

Question 11

how can the effect of concentration on rate be demonstrated?

Answer 11

reacting sodium thiosulphate solution with hydrochloric acid (disappearing cross experiment)

Question 12

how to calculate rate:

Answer 12

rate= 1/ time taken

Question 13

disappearing cross experiment method:

Answer 13

• sulphur is slowly produced
• after a while you can’t see through the mixture any longer
• this is measured by observing a black cross under the mixture
• INPUT- concentration of sodium thiosulphate
• OUTPUT- the time taken or the cross to disappear
• CONTROL- total volume of solution, concentration of HCl, temperature

Question 14

results of the disappearing cross experiment:

Answer 14

• proportional
• double the concentration= double the rate

Question 15

experiment to demonstrate the effect of temperature on rate:

Answer 15

magnesium and acid experiment

Question 16

magnesium and acid experiment results:

Answer 16

• the magnesium disappears
• INPUT- the temperature of the HCl
• OUTPUT- the time taken or Mg to disappear
• CONTROL- the mass and surface area of Mg, volume and concentration of HCl

Question 17

experiment to measure the effect of a catalyst on the rate of reaction:

Answer 17

decomposition of hydrogen peroxide
2H2O2 (aq)—–> 2H2O (l) + O2 (g)

Question 18

how does the decomposition of hydrogen peroxide experiment work?

Answer 18

• reaction is catalysed by manganese oxide which is a black solid
• causes it to take place much faster, taking only a few seconds to finish
• INPUT- which catalyst is being used
• OUTPUT- volume of O2
• CONTROL- volume and concentration of H2O2, temperature, mass and SA of catalyst